The overall goal of this project involves a synergistic approach of multi-scale modeling and experimental observation to elucidate the fundamental mechanisms underlying inositol trisphosphate (IP3)-mediated cellular Ca2+ signaling. Cytosolic Ca2+ transients ubiquitously regulate cellular functions as diverse as secretion, contraction and proliferation. Information is encoded by spatio-temporal patterns of cytosolic Ca2+ signals at scales ranging from nanometers and microseconds to micrometers and minutes, involving a hierarchy of 'phonemes' of Ca2+ generated by individual channels, channels clusters, and interactions between clusters. These levels cannot simultaneously be observed by any single experimental technique, and the shorter scales are below experimental resolution. We therefore integrate data-driven mathematical modeling together with experimental electrophysiological and imaging measurements to elucidate how 'elementary' Ca2+ events involving individual channels and clusters are triggered and coupled to produce global cellular Ca2+ signals. Specific aims are to: (i) characterize the gating and Ca permeation properties of the IP3 receptor (IP3R), and 2+ develop a predictive Markov model to account for its complex regulation by IP3 and Ca ; (ii) experimentally 2+ determine the spatial distribution and functional interactions between IP3R and apply the IP3R model to develop a stochastic cluster model based on cellular observations; (iii) determine the mechanisms underlying cluster-cluster interactions and IP3 diffusion that underlie global cellular signals. We focus on IP3 signaling in single experimentally-tractable system (human type 1 IP3R expressed in DT40 cells and native in SH-SY5Y neuroblastoma cells), and further investigate perturbations induced by Alzheimer's-causing presenilin mutations. Moreover, the experimental and theoretical tools we develop will be widely applicable, and the emergent principles will illuminate fundamental mechanisms of Ca2+ signaling in many cell types. Our group involves three Lead Investigators, with expertise and responsibilities as follows: John E. Pearson. Los Alamos. Theoretician - provide overall direction of the project and synthesis of data; construct minimal Markov model for InsP3R gating and comprehensive multi-scale cellular models. Don-On D. Mak U. Penn. Experimentalist - single-channel electrophysiological recording and modeling. Ian Parker. U.C. Irvine. Experimentalist - cytosolic Ca2+ imaging and modeling. Our results will help elucidate the mechanisms underlying complex calcium signals that regulate the normal functioning of almost all cells in the body, and whose disruption is implicated in diseases as diverse as Alzheimer's, bipolar disorder, and heart failure.